In communication devices where a transmit path and a receive path share the same antenna, an intermediate device (e.g. a duplexer) may be provided to connect the transmit path and the receive path to the antenna. For example, a duplexer may separate different frequency bands used for transmission and reception of radio frequency signals by means of frequency-selective filter elements. For example, a first frequency band may be used by the transmit path for transmitting radio frequency signals, whereas a second frequency band may be used by the receive path for receiving radio frequency signals. A distance between a frequency band for transmission and a frequency band for reception is called “duplex distance”. For example, a duplex distance may be 30 MHz for Long Term Evolution (LTE) frequency band 17. In particular, the transmit path and the receive path may be operated simultaneously, i.e., in Frequency-Division Duplexing (FDD) mode.
A duplexer should provide an adequate rejection of signal components related to transmission within a frequency band for reception. However, when a transmission signal is provided to the duplexer, leakage to the frequency band used for signal reception may occur. Thus, an undesired leakage component may be caused in a receive signal and yield significant transmit power in the receive signal. Accordingly, a signal containing a desired receive signal component and the undesired leakage component may be provided to a subsequent receiver, which may even result with the desired receive signal component being unrecoverable.
For Carrier Aggregation (CA), a receiver may comprise a single receive path for each component carrier and multiple clock domains may be used in the receiver (e.g. a dedicated local oscillator signal for a mixer of the respective receive path). Due to intermixing of frequencies from the multiple clock domains, a spur may occur at the mixer of a receive path. A spur is an undesired signal component occurring in addition to the dedicated local oscillator signal at an input of the mixer (e.g. due to crosstalk between the receive paths). Depending on the chosen carrier frequencies, the spur may have a frequency which is similar to a frequency of the undesired leakage component. Accordingly, the mixer may down-mix the undesired leakage component to the baseband due to the spur. The down-mixed leakage component may overlap with the down-mixed desired receive signal component and degrade the Signal-to-Noise-Ratio (SNR) of the baseband receive signal.
Conventional approaches attempt to mitigate the above described effects by suppressing the undesired leakage component before they can reach the mixer. In order to achieve this, elaborate layout planning of the semiconductor circuit, high electrical isolation between the various electrical components, high attenuation of the duplexer or separate flexible Surface Acoustic Wave (SAW) filters which filter out the undesired leakage component may be used. However, these (additional) high quality analog components increase a required area on a semiconductor substrate and manufacturing costs. Hence, there may be a desire for improved reduction of distortion components within a baseband receive signal.